The method consists in superposing a positive electrode, a separator, a negative electrode, and another separator, with the two separators possibly being two lengths of a common separator, in winding these items around a core thus obtaining a roll, and then inserting the spool in a can which is to constitute the negative terminal of the cell.
At the end of the winding operation, the turns of the roll must be prevented from slackening off too much, so as to be able to insert the roll in the cam.
A first prior method consists in binding the roll at the end of the winding operation by means of adhesive tape, for example, and then inserting the bound spool into the can. The major drawback of this method lies in the face that the binding remains permanently in the cell and cannot be removed.
In U.S. Pat. No. 4,099,401, the last turn of the winding is fixed to the previous turn by means of a two-faced adhesive tape. All techniques relying on adhesive tape bonding suffer from intrinsic drawbacks. Firstly it is necessary to periodically stop the winding machine in order to load a new spool of adhesive tape. Secondly, the operation of applying adhesive tape is unreliable since the tape may kink, stick to itself, stick to various parts of the machine, etc. . . . .
In addition, such an implementation which requires an operation of unwinding the adhesive tape, then a cutting operation, and then the application of a piece of tape, is incompatible with a high speed roll manufacturing rate, e.g. less than one second per roll.
A second prior method which makes it possible to omit the binding, consists in inserting the roll, after it has been wound, into a transfer ring, and then moving the ring close to the can prior to inserting the roll into the can, with the portion of the roll that is not yet inserted in the can being held by the ring. This method makes it possible to insert a roll directly into a can, but the use of such a ring after winding the roll constitutes an additional operation which requires considerable equipment.
In a third method described in U.S. Pat. No. 4,402,784, heat welding members come into contact, at the end of winding, with the outer surface of the roll in order to bond the last turn of the separator to the prior turn. This method also suffers from several drawbacks. Each welding operation requires a machine stop time, and a separator strip melting time which lasts substantially in the range 0.4 seconds to 1 second. This greatly penalizes the operating rate. Further, it is necessary to provide access for a welding tool to the center of the winding machine which is extremely difficult because of the presence of members for holding the roll. Further, it is essential for the various items to be at an accurate angle in order to perform hot welding repetitively. Finally, there is a risk of the separator sticking to the welding electrodes.
The method of the present invention avoids binding while also avoiding an additional operation after winding which could slow down the manufacturing process.
This method also prevents the turns from relaxing prior to insertion into the can, and provides a choice between releasing or not releasing the turns after they have been inserted, depending on whether a power cell or an energy cell is to be obtained.